Mercury in fish does not appear to contribute to autism, researchers reported.

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The study contributes to the growing body of literature that suggests that exposure to mercury does not play an important role in autism.

Mercury in fish does not appear to contribute to autism, researchers reported.

The finding comes from analysis of a large cohort of mothers and children in the Seychelles, an Indian Ocean nation where residents consume about 10 times the amount of ocean fish as people in the U.S., according to Edwin van Wijngaarden, PhD, of the University of Rochester Medical Center in Rochester, NY, and colleagues.

But despite prenatal methylmercury levels that were approximately 10 times those of mothers in the U. S., there was no association between methylmercury and their children's scores on autism screening tests, van Wijngaarden and colleagues reported online in Epidemiology.

The findings "contribute to the growing body of literature that suggest that exposure to the chemical does not play an important role in the onset of these (autistic) behaviors," van Wijngaarden said in a statement.

Despite that growing body of evidence, the researchers noted that there continues to be public concern that mercury exposure and autism spectrum disorder may be associated.

While vaccines and dental fillings have also been suggested as possible routes of exposure (and largely discounted by investigators), the main source of exposure to organic mercury in humans is the methylmercury found in fish, they added.

To see if too much fish during pregnancy might be associated with signs of autism, van Wijngaarden and colleagues gave the Social Communication Questionnaire to parents of a cohort of 1,784 children, adolescents, and young adults.

The 40-item questionnaire is widely used to screen people for symptoms of autism spectrum disorders; it is not a diagnostic test but a score of 15 or higher is regarded as a sign that further evaluation is warranted.

All of the mothers of members of the cohort had given a prenatal hair sample, which was available to evaluate mercury levels during pregnancy, van Wijngaarden and colleagues reported.

A subset of 532 children in the cohort were also given, at an average age or 10.7, the Social Responsiveness Scale, a 65-item scale that looks for autistic symptoms in ordinary social settings, they added.

The scale's scores range from 0 to 195, with higher scores indicating more autistic traits; a score of 70 or greater in males and 65 or greater in females indicates possible autism spectrum disorders.

The primary endpoint of the analysis was the score on the Social Communication Questionnaire related to the mother's prenatal mercury levels.

On average, the prenatal methylmercury level in the mothers was 8.4 parts per million, the researchers reported, and the average score on the Social Communication Questionnaire score was 8.0, with 8% of participants getting a score of 15 or higher.

But prenatal methylmercury exposure wasn't associated with scores on the questionnaire in multivariable linear and binomial regression modeling, van Wijngaarden and colleagues found.

On average, the prenatal methylmercury exposure for the 532 participants with Social Responsiveness Scale scores was 6.7 parts per million and the mean score was 57.6, with 34% of participants above the cut-off indicating possible autism.

But again, the regression models showed no association between mercury and the social responsiveness scores, the researchers reported.

"The Seychelles study was designed to follow a population over a very long period of time and focus on relevant mercury exposure," according to Philip Davidson, PhD, an emeritus professor at University of Rochester Medical Center and principal investigator of the overall study.

"This study shows no consistent association in children with mothers with mercury levels that were six to 10 times higher than those found in the U.S. and Europe," Davidson said in a statement. "This is a sentinel population and if it does not exist here than it probably does not exist."

The study was supported by the National Institute of Environmental Health Sciences and by the Government of the Republic of Seychelles. The journal said the authors reported no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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